Process and apparatus for making ketene



Onto 2, 1934.

G. H. REI D PROCESS AND APPARATUS FOR MAKING KETENE Filed Feb. 5; 1932 INVENTOR: ind,

Y ATTORNEYS I Acetone and acetic anhydride 25 practicability and economy is Patented Oct. 2, 1934 PROCESS AND APPARATUS FOR MAKIN KETENE George H.

signor to Reid, South Charleston, W. Va., as- Carbide and Carbon Chemicals Corporation, a corporation of New York Application February 5, 1932, Serial No. 591,151 9 Claims. (Cl. 260-134) The invention relates to a process and apparatus for making ketene (CH2:QO) by the pyrolysis of organic compounds which can be thermally decomposed to yield products including ketene. are examples of such compounds.

Ketene is a useful acetylating reagent for choice of suitable many organic syntheses, but industrial applications of the reactions of ketene have heretofore 10 been barred by the difficulties involved both in its production and utilization.

The principal object of my invention is to provide a process and apparatus for making ketene in. a simplified and economical manner which l5 largely avoids the existing difficulties in the production of ketene.

Ketene is an extremely active compound of unstable nature, and will decompose or polymerize at its formation temperature. For this reason the period during which the material from which ketene is made is exposed to cracking temperatures must be closely controlled and the temperatures of pyrolysis must be carefully regulated.

An important consideration with regard to the fact that the material with which substances which are thermally decomposed to produce ketene are in contact during the pyrolysis influence its production to a marked degree, for example, ketene can be formed from acetone by thermally decomposing the latter at temperatures between about 600 and 750 0., according to the reaction CH3.CO.CH3=CH2 I CO-l-CH4.

Because of the tendency of ketene to-be converted into other substances if allowed to remain at its formation temperature, the material of the pyrolytic chamber must be a good conductor of heat. Also, the material must be able to withstand continued heating at the cracking temperature and the accompanying oxidizing effects. These requirements for the material of the cracking chamber practically limit the available material to non-metallic refractory materials and the higher melting metals and alloys. In general,

non-metallic refractory materials are not satisfactory because of their mechanical and physical characteristics, and the list is thus restricted to metals and alloys. Early investigators have shown that iron, nickel and related metals or their alloys are unsatisfactory because they apparently exert a catalytic effect upon ketene or the pyrolytic reaction by which it is formed and cause carbon to be formed and deposited on the metal.

- Using the pyrolysis of acetone as an example, the

reaction in the presence of iron, nickel, or their alloys is probably as follows, with or without the intermediate formation ofketene:

This deleterious effect of the common heat resistant metals and alloys further restricts the materials, and leaves copper and certain of the precious metals as the only available materials. 65

Copper is satisfactory and has been successfully employed in cracking chambers for making ketene. The use of copper, however, involves many difficulties. Copper oxidizes readily at the temperatures used, which range from atmospheric temperature at the cool end of the vaporizer in a typical apparatus, to 750 C. at the outlet end of the cracking zone. For this reason, the copper must be protected from the air. This may be done by surrounding the copper equipment in an inert or reducing atmosphere, or by providinga sheath or shell of a more resistant metal or alloy over the copper tubes. Either .method of protection is difficult and makes the production of ketene expensive. The fabri- 8o cation of duo-metal cracking chambers in which copper forms the inner portion is further complicated by the thermal expansion of copper which is greater than that of iron or its alloys.

My invention minimizes these difficulties and its advantages are apparent. The invention broadly comprises the use of an apparatus which does not employ copper except for the zone of actual pyrolysis. For temperatures up to and including temperatures at which incipient cracking occurs I have discovered that iron alloys containing a substantial proportion of chromium may be used without causing carbon deposition or otherwise deleteriously affecting the reactions. I prefer to use those alloys of iron and chromium which contain more than about 10% of chromium but which may contain up to about 30% of chromium and which are free from nickel, but other heat and oxidation resistant alloys may be used.

The method of practicing my invention will be apparent'from the following description and the accompanying drawing which is a diagram-' matic lay-out of apparatus (partially in section) embodying my invention.

The substance to be thermally decomposed to yield ketene, e. g. acetone, is supplied from a storage tank 9 by means of a pipe 10 and pressure is supplied thereto by a pump 11. The pipe 10 is connected to a vaporizer section 12 within 110 a furnace 13. The furnace 13 is provided with heating means, such as a gas burner 20 supplied with gaseous fuel by a pipe 21 and a valve 22 to control the flow of the fuel. The vaporizer 12 may be formed of steel, iron or any convenient metal or alloy and is of suflicient length and heated sufiiicently to vaporize the acetone and to heat thevapors to a temperature which, assuming throughout this description that acetone is being cracked, does not exceed about 300 C. at a point 14. From the vaporizer 12 the vapor is passed into a tube 15 which is formed of a heat and oxidation resistant alloy or metal free from nickel, for example, chrome-iron (26% to 29% Cr.). The tube 15 is of sufiicient length and is heated so that the vapors are heated to or slightly above about 500 C. where incipient cracking of the acetone will occur. This temperature may be as high as 550 or 575 C. at a point 16. From the tube 15 the vapors, now at a stage approximating cracking conditions, are passed into a cracking tube 17. From the cracking tube 17 the cracked products of pyrolysis including ketene are removed from the furnace 13 by a pipe 19 to be utilized. The tube 17 is preferably made of copper, but other materials having the requisite properties for the pyrolysis of acetone and which do not deleteriously afiect the reaction as defined above may be used. The copper cracking tube 17 as shown. is protected by a shell 18 formed of a metal or alloy which is more resistant to high temperatures and to oxidation than is copper, e. g. chrome-iron or the like may be used. Instead of the shell 18 other protective means may be used. The protective means for the cracking tube is not an essential part of my invention.

By the use of my invention including the apparatus above described the expensive and difficult manipulation of copper for the production of ketene is minimized and I provide a'process for producing ketene under conditions which do not cause carbon deposition and which includes the use of materials which were previously considered to be desirable but which hereheated chrome-iron tube equipped with pyrometers for measuring the temperature both within and outside of the tube wall. When the inside temperature was 535 C. and the outside temperature was 585 C. the first permanent gas was formed. This gas had no odor of ketene. The temperatures were then raised gradually until the inside temperature was 585 C. and the outer temperature was 630 0. During the time of the test a very small amount of gas was given off and the amount of ketene was small. At the end of the test over 96% of the-acetone passed through the tube was recovered as condensate, and the tube was found to be almost entirely free from deposited carbon.

In operating my process I prefer to maintain a positive gage pressure of about 5 pounds per square inch on the apparatus, with an inlet temperature of the gas to the cracking zone of about 550 to 575 C., and an outlet temperature for the vapors of about 650 C. when acetone is being cracked. The contact time of the vapors with cracking temperatures preferably should be between about 0.25 and about 0.75 seconds. That is, the vapors preferably have a space velocity in the cracking zone of about 2500 to about 3500 liters of vapor per liter of volume in the cracking zone per hour. The conversion of acetone to ketene under these conditions is about 15% to 22% per pass. While the foregoing conditions have been found to be desirable, they may be varied within a considerable range. The temperature in the zone of actual pyrolysis should be between about 600 and 750 C., and pressures and gas velocities should be used which will permit the contact time of the vapors to be kept within the above limits.

I claim:-

1. An apparatus for thermally decomposing organic substances to obtain products including ketene which comprises a series of metallic chambers, one of which is composed of an alloy of iron and chromium and which immediately precedes and is connected to the last of said chambers in the series, said last chamber being composed of a metallic material consisting predominantly of copper, the whole of said series forming a single continuous passage, means for supplying the substance to be decomposed to said series of chambers, means for removing the products including ketene from said last chamber, and means for heating said chambers.

2. An apparatus for thermally decomposing organic substances to obtain products including ketene which comprises a series of metallic chambers, one of which is composed of an alloy of'iron and chromium containing between about 10% and about 30% chromium and which immediately precedes and is connected to the last of said chambers in the series, said last chamber being composed of a metallic material consisting predominantly of copper, the wholeof'said series forming a single continuous passage, means for supplying the substance to be decomposed to said series of chambers, means for removing the products including ketene from said last chamber, and means for heating said chambers.

3. An apparatus for thermally decomposing in organic substances to obtain products including ketene which comprises a series of metallic chambers, one of which is composed of an alloy of iron and chromium and which immediately precedes and is connected to the last of said chambers, said last chamber being composed of copper, the whole of said series forming a single continuous passage, means for protecting said last chamber from oxidizing conditions, means for vsupplying the substance to be decomposed to 130 organic substances to obtain products'including ketene which comprises a series of metallic chambers, one of which is composed of an alloy of iron and. chromium and which immediately precedes and is connected to the last of said chambers, said last chamber being composed of 14g copper and provided with a shield of heat resistant metal to protect said copper chamber from oxidizing conditions, the whole of said series forming a single continuous passage, means for supplying the substance to be decomposed to said series, means for removing the products including ketene from said last chamber, and means for heating said chambers.

5. Process for making ketene which comprises passing organic substances which can be decomposed to yield products including ketene successively through a chamber formed of an alloy of iron and chromium which is heated to the lowest temperature decomposition of said substances is initiated, and then through a metallic chamber composed predominantly of copper I tree from iron and nickel, which is heated to a temperature such that said substances are decomposed into products including ketene.

6. Process for making ketene which comprises passing acetone vapors successively through a chamber formed of an alloy of iron and chromium containing between about 10% and about 30% chromium which is heated to a temperature not exceeding about 550 C. and then through a chamber composed essentially of copper and heated to between about 600 and 750 C.

'7. Process for making ketene which comprises passing acetone vapors successively through a chamber formed of an alloy of chromium and iron which is heated to a temperature not exceeding about 550 C. and then through a chamber formed of copper which is heated to between about 600 and about 750 C. said acetone vapors being under about 5 pounds per square inch of gage pressure.

8. Process for making ketene which comprises passing acetone vapors successively through a chamber formed of an alloy of chromium and iron which is heated to a temperature not exceeding about 550 C., and then through a chamber formed of copper which is heated to between about 600 and about 750 C., said acetone vapors being under about 5 pounds per square inch of gage pressure, and having a maximum space velocity through said chambers of between about 2500 and 3500 liters per liter per hour.

9. Process for making ketene which comprises passing acetone vapors successively through a chamber formed of an alloy of chromium and iron containing more than about 10% of chromium, which is heated to a temperature not exceeding about 550 C., and then through a chamber formed of copper which is heated to between about 600 and about 750 C., said acetone vapors being under about 5 pounds per square inch 01' gage pressure, and having a maximum space velocity through said chambers of between about 2500 and 3500 liters per liter per hour.

GEORGE H. REID. 

